ZM241385 is an antagonist of the facilitatory responses produced by the A2A adenosine receptor agonists CGS21680 and HENECA in the rat hippocampus

1. In the present study, we investigated the ability of a recently introduced non-xanthine A2A receptor antagonist, ZM241385 (4-(2-[7-amino-2-(2-furyl[1,2,4]-triazolo[2,3-a[1,3,5]triazin-5-yl -aminoethyl)phenol) to displace binding of the prototypical A2A Adenosine Receptor Agonist [3H]CGS21680 (2-[4-(2-p-carboxyethyl)phenylamino]-5'-N-ethylcarboxamidoadenosine) and to modify the facilitatory responses caused by the A2A selective agonists, CGS21680 and HENECA (2-hexynl-5'-N-ethylcarboxamidoadenosine) in rat hippocampal preparations. 2. ZM241385 was nearly equipotent to displace [3H]CGS21680 (30 nM) binding to hippocampal (Ki of 0.52 nM) and to striatal membranes (Ki of 0.35 nM), whereas HENECA was a more potent displacer of [3H]CGS21680 binding to striatal (Ki of 4.5 nM) than to hippocampal membranes (Ki of 19 nM). 3. HENECA (3-30 nM) was equipotent with CGS21680 to facilitate veratridine-evoked [3H]acetylcholine release from superfused hippocampal synaptosomes and ZM241385 (20 nM) inhibited the facilitatory effects of both HENECA (30 nM) and CGS21680 (30 nM); this antagonism was mimicked by CSC (250 nM). 4. In contrast, CGS21680 (10-30 nM) was more potent than HENECA (10-30 nM) to facilitate synaptic transmission in Schaffer fibres/CA1 pyramid synapses of hippocampal slices and the facilitatory effect of CGS21680 (10 nM) was blocked by ZM241385 (20 nM) whereas CSC (250 nM) caused a 40% attenuation of this CGS21680-induced facilitation. 5. These results indicate that ZM241385 is the first A2A antagonist with equal potency to displace [3H]CGS21680 binding to striatal and limbic regions, and with general efficiency to antagonize HENECA- or CGS21680-mediated facilitatory responses in the hippocampus.